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    SubjectRe: [PATCH] drm/nouveau/platform: fix compilation if !CONFIG_IOMMU
    On Wed, May 20, 2015 at 03:10:24PM +0900, Alexandre Courbot wrote:
    > The lack of IOMMU API support can make nouveau_platform_probe_iommu()
    > fail to compile because struct iommu_ops is then empty. Fix this by
    > skipping IOMMU probe in that case - lack of IOMMU on platform devices
    > is sub-optimal, but is not an error.
    >
    > Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
    > ---
    > This is an alternative to https://lkml.org/lkml/2015/5/19/484. Most users
    > of Nouveau do not care about IOMMU support, so we should not impose that
    > option on them.
    >
    > drm/nouveau/nouveau_platform.c | 16 ++++++++++++++++
    > 1 file changed, 16 insertions(+)
    >
    > diff --git a/drivers/gpu/drm/nouveau/nouveau_platform.c b/drivers/gpu/drm/nouveau/nouveau_platform.c
    > index 775277f1edb0..dcfbbfaf1739 100644
    > --- a/drivers/gpu/drm/nouveau/nouveau_platform.c
    > +++ b/drivers/gpu/drm/nouveau/nouveau_platform.c
    > @@ -92,6 +92,8 @@ static int nouveau_platform_power_down(struct nouveau_platform_gpu *gpu)
    > return 0;
    > }
    >
    > +#if IS_ENABLED(CONFIG_IOMMU_API)
    > +
    > static void nouveau_platform_probe_iommu(struct device *dev,
    > struct nouveau_platform_gpu *gpu)
    > {
    > @@ -158,6 +160,20 @@ static void nouveau_platform_remove_iommu(struct device *dev,
    > }
    > }
    >
    > +#else
    > +
    > +static void nouveau_platform_probe_iommu(struct device *dev,
    > + struct nouveau_platform_gpu *gpu)
    > +{
    > +}
    > +
    > +static void nouveau_platform_remove_iommu(struct device *dev,
    > + struct nouveau_platform_gpu *gpu)
    > +{
    > +}
    > +
    > +#endif
    > +

    Since these are all static functions, perhaps an "if (IS_ENABLED(...))"
    would work here? That way you'd get compile coverage of the code in all
    cases.

    But perhaps that doesn't work for IOMMU. I have a vague memory of
    running across something like this before and IOMMU has this quirk of
    defining struct iommu_ops as empty if IOMMU_API is deselected so you'll
    probably get compiler errors unless you actually preprocess the code
    out.

    Thierry
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